This application claims the benefit of Japanese Patent Application Number 2002-124787 filed on Apr. 25, 2002, the entirety of which is incorporated by reference.
1. Field of the Invention
The present invention relates to a screw tightening apparatus for tightening screws such as a bolt and a nut to a work.
2. Description of the Related Art
As an apparatus for automatically tightening screws, an apparatus having a nut runner provided on a free end portion or an arm of an articulated robot is known. The nut runner is usually provided with a driving motor, and a bit portion fixedly mounted on a driving shaft of the driving motor. When the driving motor is rotated with a bolt and a nut fitted around the bit portion, the tightening of the bolt and the like is done at a high speed with ease.
In such a conventional screw tightening apparatus, the robot supporting the nut runner receives via the nut runner a working force (reaction force) with respect to the tightening of a bolt and the like. Therefore, an arm has to be of a high rigidity so that even a free end portion of the arm can withstand the reaction force. As a result, the use of such a large-sized robot becomes necessary. The use of such a robot requires a large space, and costs much.